1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus such as an electrostatic transfer type copying machine and laser printer, and more particularly, to an electrophotographic image forming apparatus comprising a cleaning means for cleaning an intermediate transfer body.
2. Description of the Related Art
In a conventional electrostatic transfer type copying machine, there is generally arranged a photoconductive body cleaning means having a cleaner blade for removing developer (referred to as toner hereinafter) remaining on a photoconductive body after a visible toner image formed on the surface of the photoconductive body is transferred onto a copying paper. When the cleaner blade of the cleaning means is contacted onto the surface of the photoconductive body, the toner remaining thereon can be removed.
Recently, there is proposed an electrostatic transfer type full color copying machine comprising an intermediate transfer body onto which respective color toner images are transferred temporarily. In the full color copying machine, respective colors of toner images are transferred sequentially and superimposed on the intermediate transfer body primarily so as to form a full color toner image thereon. Thereafter, the full color toner image is transferred onto a copying paper secondarily.
In the full color copying machine comprising such an intermediate transfer body, after one color toner image formed on the photoconductive body has been transferred onto the intermediate transfer body primarily, the toner remaining on the photoconductive body is removed by a blade type photoconductive body cleaning means.
On the other hand, after the full color toner image superimposed on the intermediate transfer body has been transferred onto a copying paper secondarily, the toner may remain on the intermediate transfer body. When the intermediate transfer body is left as it is, the quality of the image to be transferred onto the copying paper is lowered due to the residual toner. Therefore, it is necessary to comprise a cleaning means for removing the toner remaining on the intermediate transfer body.
In a conventional full color copying machine, a cleaner brush is provided as the cleaning means for cleaning the intermediate transfer body. Therefore, a relatively large space is needed for arranging the cleaning means. Also, since the toner tends to adhere to the cleaner brush, it is necessary to scrape off the toner often. Furthermore, it is necessary to remove the toner scraped off by using an absorption apparatus etc., resulting in that the copying machine comprising the cleaner brush inevitably becomes bulky.
For example, it is considered that another cleaner blade having an essentially same composition as that of the cleaner blade for cleaning the photoconductive body is used as the cleaning means for cleaning the intermediate transfer body. However, it is found out that the following problems are caused when another cleaner blade is used as the cleaning means for cleaning the intermediate transfer body.
Namely, in order to avoid damages of the photoconductive body due to the contact of the cleaner blade thereto, the photoconductive body is made of an organic photoconductive conductor so that the surface thereof is not marred by the cleaner blade, and the surface thereof is finished in a mirror-like smooth surface state so that the residual toner can be scraped off therefrom easily and the toner image formed thereon can be transferred easily. As a result, since the cleaner blade removes the toner remaining on the surface of the photoconductive body by slidably contacting to the mirror-like smooth surface thereof, the contact pressure of the cleaner blade to the photoconductive body is set at a relatively low value generally. And, the friction coefficient between the cleaner blade and the surface of the photoconductive body is set at a relatively small value of about 1.0 so that the toner can be surely removed.
However, when the cleaner blade having an essentially same composition as that of the cleaner blade for cleaning the photoconductive body is used as the cleaning means for cleaning the intermediate transfer body, the cleaning performance for cleaning the intermediate transfer body is lowered considerably, and the cleaner blade tends to be reversed according to the movement of the intermediate transfer body. Furthermore, a large friction is caused on the edge portion of the cleaner blade. Therefore, a stable cleaning performance for cleaning the intermediate transfer body can not be obtained.